Heretofore, it has been the practice to produce a dentition model for producing a crown or bridge for dental therapy purposes, by replicating the objective tooth by taking an impression of the dentition including the ambient area around the objective tooth, followed by plaster molding. The so-prepared model of the die is then processed in a dental laboratory by a dental technician to settle reference planes by trimming the tooth end and each face with a trimmer, whereupon a dowel pin is placed on the bottom face of the reference plane by a dowel pin drill or dowel pin setter and is fixed with an adhesive or plaster. Then, a groove is formed on the outer or inner face of the dowel pin for preventing rotation thereof. The groove is formed by cutting with a point, whereupon this is coated with a release compound. The resulting removable die model is embedded in a mass of secondary pour plaster filled in a rubber case, in such a manner, that the upper part of the model above the row of dowel pins sinks beneath the upper face of the plaster. After the plaster has hardened, the plaster block is taken out of the rubber case and is cut off to leave the portion of the objective die. Then, the model of the objective die is separated from the cut portion by withdrawing it therefrom. The die of the abutment tooth is worked up by trimming into a finished shape permitting easy fit of a crown, bridge or the like. The so-trimmed die is then placed in the proper position on the tray of secondary pour plaster and is used for preparing the corresponding crown or bridge by adjusting the relative posture to the neighboring tooth dies and adjusting the engagement with the opposing tooth to be engaged therewith.
Also for producing an all ceramic denture, the model entire act of teeth is first prepared using a silicone rubber impression material and replicating with a refractory material therefrom to produce renewedly the working cast. Here, the expensive heat resistant dowel pins used in these work procedures have to be handed over to the dental surgeon without removing them.
As explained above, the prior art technique requires the cost of the entire die of teeth for preparing the objective abattment tooth, so that a large amount of expensive material has to be employed for the preparation. Such material cost is especially high for all ceramic dentures using silicone impression material and refractory cast material. In addition, the prior art operates to finish the crude die model by trimming, whereby its original contour is altered, which makes it difficult to recognize the actual position of ginvals around the reference planes of the die and the transition areas therebetween, when the unprocessed denture to be prepared, such as, a crown or the like, is placed on the working model for the adjustment work thereof.